BALTIMORE, June 15 -- Why Houston's Morgan Ensberg stopped running, the Baltimore Orioles didn't really know. Did he think he had a hit? Had he suddenly pulled up lame?

Either way, the blessing of the night for a Baltimore team that has seemed blessed all season came on the fifth batter of the game, when Ensberg rolled what seemed to be a run-scoring single over second base. Only the Orioles' Brian Roberts came flying from nowhere, sprawling across the grass, diving, lunging and finding the ball stuck in his glove.

He rolled on his back, crawled to his knees. He looked toward first.

"I don't even know why I bothered to throw it," he said.

But he threw anyway. Just as Ensberg stopped, coming to a halt inches before the base. The ball plopped into first baseman Jay Gibbons's mitt. Inning over and the Orioles never felt so lucky.

Shortstop Miguel Tejada shouted and clapped his hands. Pitcher Rodrigo Lopez smiled. And an inning that could have buried Baltimore early ended without a blemish and might just have been the thing that propelled the Orioles to a sweep of the Astros with a 5-1 victory Wednesday night.

"When you make a play like that, it pumps a team up," Orioles Manager Lee Mazzilli said. "Sometimes something as little as that might set the tone."

Someday Lopez might want to thank Ensberg. For the Orioles, inspired, went right after Houston starter Wandy Rodriguez, scoring twice in the first and two more times in the second to give Lopez much more than he would need. The Astros had runners on first and third with two out when Ensberg hit his grounder. The runner on third, Orlando Palmeiro, trotted toward the plate. The runner on first, Craig Biggio, steamed toward second.

For a moment Lopez thought Roberts might have a play on Biggio but he soon realized the futility of that hope. Then he saw Ensberg stop short of first and felt nothing short of elation.

"That was great for all of us," Lopez said. "It pushed it up for us. Then we came back to score two runs; that was huge."

Or as Roberts said, "It goes from 1-0 to 2-0 the other way."

Saved from what could have been a dreadful opening inning and then given the big lead, Lopez was almost untouchable the rest of the night. He has struggled at times this year, pitching brilliantly in one start and looking awful in the next. But lately he has improved, allowing two runs or less in four of his last five starts. He hasn't lost since May 19.